Devices comprising electric motors, for example washing machines comprising an electrical motor that drives a drum via a belt drive, often are operated in the so-called field-weakening range in order to control the rotational speed and to achieve the required rotational speed of the drive. In view of efficiency considerations of the drive system electrical motors comprising permanent solenoid excitation are preferred.
Typically the electrical motor is controlled by circuitry responsible for power supplying and controlling the electrical motor in the drive, i.e., controlling the rotational speed of the motor. The supply and control circuitry itself requires a power supply.
In case of a failure in the drive system the power supply for the control circuitry may be affected in that the power supply for the control circuit is shut off or the supply voltage drops significantly, so in both cases power supply of the control circuit breaks down.
Conventional solutions provide some kind of sources for providing power supply in that event, for example large capacitors or rechargeable batteries can be provided. However, these emergency power supply sources are costly and typically require a comparatively large area on a printed circuit board or within an integrated circuit.